IT was while the Great Ice King still ruled over all America from the pole to the middle United States that Lake Lahontan and Lake Bonneville spread their waters over hundreds of square miles of our western territory; Lahontan where we now have the sage plains and alkali sinks of Nevada, and Bonneville covering the greater part of Utah west of the Wasatch Mountains, but now reduced to Sevier, Utah, and Great Salt Lakes, the last shallow remnants of a once mighty inland sea. It was probably long before these great lakes had dried up, while their waters were yet fresh and sweet, that occurred an event which wrought a vast change in the physical geography of that region. Somewhere, but no one is yet certain exactly where, one or more great fissures opened in the earth, and there poured out an incredible amount of lava which covered not less than one hundred and fifty thousand square miles with one vast sheet of rhyolite hundreds, in some places thousands, of feet in thickness. Northern California, northwestern Nevada, nearly all of Oregon, Washington, and Idaho, and parts of Wyoming, the Yellowstone Park, Montana, and British Columbia were all covered by this stupendous flow.

The effect of this lava flow upon the present distribution of the fishes of that region is known to have been very great, and we are now beginning to understand some of the most important factors of that distribution—a distribution which, until recently, presented many anomalies.

It has been my good fortune to make explorations in Montana, Wyoming, Idaho, and the Yellowstone Park which have cleared up some of these difficulties. The presence of trout in Yellowstone Lake and the total absence of all fish from the other large lakes of the park was one of the most interesting of these anomalies, and it is to its explanation that this article is devoted.

It is certain that all the streams and lakes of the territory covered by the lava flow were wiped out of existence by the fiery flood, and all terrestrial and aquatic life destroyed. Many long years must have passed before this lava sheet became sufficiently cooled to permit the formation of new streams; but a time finally came when the rains, falling upon the gradually cooling rock, were no longer converted into steam and thrown back into the air, only to condense and fall again, but, being able to remain in liquid form upon the rock, sought lower levels, and thus new streams began to flow. And then the fishes in the connecting streams below, which had not been destroyed by the lava flow, began to invade the desolated region and repeople its waters.

The rhyolite, obsidian, and trachyte were very hard and eroded slowly, but when the streams reached the edge of the lava field they encountered rock which was comparatively soft and which wore away rapidly. The result is that every stream leaving the Yellowstone Park has one or more great waterfalls in its course where it leaves the lava sheet. Notable among these streams are Lewis River, the outlet of Lewis and Shoshone Lakes; Yellowstone River, the outlet of Yellowstone Lake; Gardiner, Gibbon, and Firehole Rivers, and Lava, Lupine, Glen, Crawfish, Tower, and Cascade Creeks, all leaving the lava sheet in beautiful falls, varying from thirty feet to over three hundred feet in vertical descent. The following is a list of the principal waterfalls in the streams in and about the park, each one of which is supposed to form an insurmountable barrier to the ascent of fish:

Great Falls of the Yellowstone

308

feet.

Upper Falls of the Yellowstone

109

"

Crystal Falls in Cascade Creek

129

"

Tower Falls in Tower Creek

132

"

Undine Falls in Lava Creek

60

"

Lower Falls in Lava Creek

50

"

Wraith Falls in Lupine Creek

100

"

Osprey Falls in Gardiner River

150

"

Rustic Falls in Glen Creek

70

"

Virginia Cascades in Gibbon River

60

"

Gibbon Falls in Gibbon River

80

"

Keppler Cascade in Firehole River

80

"

Upper Falls in Lewis River

50

"

Lower Falls in Lewis River

30

"

Moose Falls in Crawfish Creek

30

"

Two-Ocean Pass, Looking East.

Besides these, there are almost innumerable falls in the smaller streams and brooks, but of them we take no account. When it is remembered that nearly all these falls are within the limits of an area fifty-five by sixty-five miles, one can get some idea of the grandeur and beauty of the Yellowstone National Park. It is doubtful if any other similar area in the world affords so many magnificent waterfalls, beautiful cascades, seething torrents, and abysmal gorges as are found here. But these are among the least of the strange and wonderful things in this wonderland, where geysers great and small, mud springs and boiling paint-pots, and petrified forests so abound. With scarcely an exception all these streams and lakes are of the best of pure, clear, cold water, well supplied with insect larvæ, the smaller crustacea, and various other kinds of the smaller animal and plant forms sufficient in amount to support an immense fish life. But it is a strange and interesting fact that, with the exception of Yellowstone Lake and River, these waters were wholly barren of fish life until recently stocked by the United States Fish Commission. The river and lake just named are well filled with the Red-throated trout (Salmo mykiss lewisi), and this fact is the more remarkable when it is remembered that the falls in the lower Yellowstone River are one hundred and nine and three hundred and eight feet, respectively—by far the greatest found in the park.

The total absence of fish from Lewis and Shoshone Lakes and the numerous other small lakes and streams of the park is certainly due to the various falls in their lower courses, which have proved impassable barriers to the ascent of fishes from below; for in every one of these streams, just below the falls, trout and in some cases other species of fishes are found in abundance. But to account for the presence of trout in Yellowstone Lake was a matter of no little difficulty. If a fall of thirty to fifty feet in Lewis River has prevented trout from ascending to Lewis and Shoshone Lakes, why have not the much greater falls in the Yellowstone proved a barrier to the ascent of trout to Yellowstone Lake? Certainly no fish can ascend these falls, and we must look elsewhere for the explanation.

Many years ago the famous old guide, Jim Bridger, told his incredulous friends that he had found, on the divide west of the upper Yellowstone, a creek which flowed in both directions one end flowing east into the Yellowstone, the other west into Snake River. But, as he also told about many other strange and to them impossible things which he had seen—among which were a glass mountain, and a river which ran down hill so fast that the water was made boiling hot—they were not disposed to acknowledge the existence of his "Two-Ocean Creek." Subsequent events

Upper Falls of the Yellowstone River. One hundred and nine feet.

however, showed that the strange stories of Jim Bridger were not without some elements of truth.

Two-Ocean Pass was visited by Captain Jones in 1873, by Dr. F. V. Hay den in 1878, and by Mr. Arnold Hague in 1884. The observations made by these various explorers seemed to indicate that Two-Ocean Pass is a nearly level meadow, near the center of which is a marsh, which, in times of wet weather, becomes a small lake, and that "a portion of the waters from the surrounding mountains accumulates in the marshy meadows and gradually gravitates from either side into two small streams, one of which flows to the northeast, the other to the southwest" (Hayden).

From these reports it began to be suspected that trout, ascending Pacific Creek from Snake River, might, in time of high water, pass through the lake in Two-Ocean Pass and descend Atlantic Creek and the upper Yellowstone to Yellowstone Lake, and thus would the origin of the trout of that lake be explained. Dr. Jordan, who spent some time in the park in 1889, was impressed with the probable correctness of this explanation, but did not visit Two-Ocean Pass.

In 1891, while carrying on certain investigations in Montana and the Yellowstone Park, under the direction of the United States Commissioner of Fish and Fisheries, Colonel Marshall McDonald, I was instructed to visit Two-Ocean Pass and determine definitely the conditions which obtain there.

On August 7th, with Billy Hofer, that prince of mountaineers, as our guide, we started out from the Mammoth Hot Springs with a pack train of ten pack horses and eight saddle horses. Our route led us through all the geyser basins of the park, and we reached Two-Ocean Pass August 17th, where we remained long enough to make a careful examination.

This pass is a high mountain meadow, about eight thousand two hundred feet above the sea, and situated just south of the park, in longitude 110º 10΄, latitude 44º 3΄. It is surrounded on all sides by rather high mountains, except where the narrow valleys of Atlantic and Pacific Creeks open out from it. Running back among the mountains to the northward are two small cañons, down which come two small streams. On the opposite side is another canon, down which comes another small stream. The extreme length of the meadow from east to west is about a mile, while the width from north to south is not much less. The larger of the streams coming in from the north is Pacific Creek, which, after winding along the western side of the meadow, turns abruptly westward, leaving the pass through a narrow gorge. Receiving numerous small affluents, Pacific Creek soon becomes a good-sized stream, which finally unites with Buffalo Creek a few miles above where the latter stream Hows into Snake River.

Shoshone Lake, North Shore

Yellowstone Lake.

Atlantic Creek was found to have two forks entering the pass. At the north end of the meadow is a small wooded canon, down which flows the North Fork. This stream hugs the border of the flat very closely. The South Fork comes down the cañon on the south side, skirting the brow of the hill a little less closely than does the North Fork. The two, coming together near the middle of the eastern border of the meadow, form Atlantic Creek, which, after a course of a few miles, flows into the Upper Yellowstone. But the remarkable phenomena exhibited here remain to be described.

Each fork of Atlantic Creek, just after entering the meadow, divides as if to flow around an island; but the stream toward the meadow, instead of returning to the portion from which it had parted, continues its westerly course across the meadow. Just before reaching the western border the two streams unite, and then pour their combined waters into Pacific Creek; thus are Atlantic and Pacific Creeks united, and a continuous water way from the mouth of the Columbia, via Two-Ocean Pass, to the Gulf of Mexico is established. Two-Ocean Creek is not a myth but a verity, and Jim Bridger is vindicated. We stood upon the bank of either fork of Atlantic Creek, just above the place of the "parting of the waters," and watched the stream pursue its rapid but dangerous and uncertain course along the very crest of the "Great Continental Divide." A creek flowing along the ridgepole of a continent is unusual and strange, and well worth watching and experimenting with. So we waded to the middle of the North Fork, and, lying down upon the rocks in its bed, we drank the pure icy water that was hurrying to the Pacific, and, without rising, but by simply bending a little to the left, we took a draught from that portion of the stream which was just deciding to go east, via the Missouri-Mississippi route, to the Gulf of Mexico. And then we tossed chips, two at a time, into the stream. Though they would strike the water within an inch or so of each other, not infrequently one would be carried by the current to the left, keeping in Atlantic Creek, while the other might be carried a little to the right and enter the branch running across the meadow to Pacific Creek; the one beginning a journey which will finally bring it to the great gulf, the other entering upon a long voyage in the opposite direction to Balboa's ocean.

Pacific Creek is a stream of good size long before it enters the pass, and its course through the meadow is in a definite channel; but not so with Atlantic Creek. The west bank of each fork is low, and the water is liable to break through anywhere, and thus send a part of its water across to Pacific Creek. It is probably true that one or two branches always connect the two creeks under ordinary conditions, and that, following heavy rains, or when the snows are melting, a much greater portion of the water of Atlantic Creek finds its way across the meadow to the other.

Besides the channels already mentioned, there are several more or less distinct ones that were dry at the time of our visit. As

already stated, the pass is a nearly level meadow, covered with a heavy growth of grass and many small willows one to three feet high. While it is somewhat marshy in places, it has nothing of the nature of a lake about it. Of course, during wet weather the small springs at the borders of the meadow would be stronger; but the important facts are that there is no lake or even marsh there, and that neither Atlantic nor Pacific Creek has its rise in the meadow. Atlantic Creek, in fact, comes into the pass as two good-sized streams from opposite directions, and leaves it by at least four channels, thus making an island of a considerable portion of the meadow. And it is certain that there is, under ordinary circumstances, a continuous waterway through Two-Ocean Pass of such a character as to permit fishes to pass easily and readily from Snake River over to the Yellowstone, or in the opposite direction. Indeed, it is possible, barring certain falls in

Diagram showing Relation of Streams in Two-Ocean Pass.

Snake River, for a fish so inclined to start at the mouth of the Columbia, travel up that great river to its principal tributary, the Snake, thence on through the long, tortuous course of that stream, and, under the shadows of the Grand Tétons, enter the cold waters of Pacific Creek, by which it could journey on up to the very crest of the Great Continental Divide to Two-Ocean Pass; through this pass it may have a choice of two routes to Atlantic Creek, in which the down-stream journey is begun. Soon it reaches the Yellowstone, down which it continues to Yellowstone Lake, then through the lower Yellowstone out into the turbid waters of the Missouri. For many hundred miles it may continue down this mighty river before reaching the Father of Waters, which will finally carry it to the Gulf of Mexico—a wonderful journey of nearly six thousand miles, by far the longest possible fresh-water journey in the world.

We found trout in Pacific Creek at every point where we examined it. In Two-Ocean Pass we obtained specimens from each of the streams, and in such positions as would have permitted them to pass easily from one side of the divide to the other. We also caught trout in Atlantic Creek below the pass, and in the upper Yellowstone, where they were abundant.

Thus it is certain that there is no obstruction even in dry weather to prevent the passage of trout from the Snake River to Yellowstone Lake; it is quite evident that trout do pass over in this way; and it is almost absolutely certain that Yellowstone Lake was stocked with trout from the west, via Two-Ocean Pass.

From the basin of Snake River above Shoshone Falls we know at least twelve different species of fishes, but of all these the trout is the only one which has been able to pass over the Continental Divide and establish itself in Yellowstone Lake and its tributary streams, for no other species is known from those waters. But these twelve species are, as a rule, fishes of intermediate altitudes, rarely ascending into streams so cold as Pacific Creek. The only one which accompanies the trout into Pacific Creek is the blob (Cottus bairdi punctulatus), which we found even in Two-Ocean Pass, but it has never been seen on the Yellowstone side of the pass.